Full Converter Research Articles

Operation Analysis of Power Systems with HVDC Interconnections Using a Transient Stability Aware OPF Method

High-voltage direct current (HVDC) transmission systems are widely used today due to their several advantages over high-voltage alternative current (HVAC) systems. They are primarily utilized in connecting different large grids or smaller independent networks, especially in submarine interconnections. Many studies have been conducted globally on the optimal planning, operation, and control of these power systems. Understanding the transient stability of these systems during significant disturbances is also of great importance. This paper specifically focuses on power systems with HVDC connections and high penetration of renewable energy sources. Analytical models were developed for power system components like HVDC converters, DC lines, and full converter wind generators. A simulation of a test-case power system was conducted, including various significant disturbances such as HVDC line trips, short circuits, power unit failures, and major changes in load. The voltage and frequency stability of the system under specific operational scenarios was also examined. The results obtained indicate technical limitations and operating guidelines to avoid undesirable conditions and system failure. In conclusion, adopting short-term stability tests the optimal operation point of the system, and the limitations in the penetration by RES units can be decided.

Mitigation of severe false data injection attacks (FDIAs) in marine current turbine (MCT) type 4 synchronous generator renewable energy using promoted backstepping method

False data injection attack (FDIA) is kind of the most important and prevalent cyber attacks, influencing in power systems and renewable energy resources in microgrids (MGs). The destructive effects caused by FDIAs in the voltage components of synchronous generator with full converter in AC microgrid (ACMG) renewable energy production would seriously damage the DC link voltage, network frequency and also, the active power. The extracted voltage components in the d and q axes to control the grid side converter (GSC) as the main control section, are the important signals for power control process of the synchronous generator with wind or marine current turbine (MCT). In this regards and due to the nonlinear behavior caused by cyber attacks in the generator control process, the robust performance of modified nonlinear backstepping method would be an appropriate alternative, instead of the conventional linear control including PI controllers. Thus, a remedial action against various FDIAs caused in the voltage control commands of the GSC is proposed. Moreover, promotion of the backstepping control by combining with the switching terms, adopted from the higher order super twisting sliding mode control (HOSTSMC), the performance of the proposed method would be precisely robust. To verify the proposed method, severe FDIAs by injecting various constant values, periodic and also, noisy signals are our case studies which are simulated via MATLAB software in the weak grid connect and standalone operation modes.

A Megawatt-Scale Si/SiC Hybrid Multilevel Inverter for Electric Aircraft Propulsion Applications

This paper presents the design and development of a megawatt-scale medium-voltage (MV) hybrid inverter prototype to validate its feasibility and potentials for the electric propulsion on the next-generation electric aircraft system with an onboard MV dc distribution, e.g., 3 kV dc bus in this work. The proposed hybrid converter consists of a three-level active-neutral-point-clamped (ANPC) stage using 3.3 kV silicon IGBTs cascaded with an H-bridge stage using cost-effective 1.2 kV SiC MOSFETs in each phase. Comprehensive design and evaluation of the full-scale prototype are elaborated, including the low-inductance busbar design, converter architecture optimization and system integration. In addition, a low computational cost space vector modulation with common-mode voltage (CMV) reduction feature is proposed to fully exploit the benefits of SiC MOSFET in this hybrid topology. Extensive simulation and experimental results are provided to demonstrate the performance of each power stage and the full converter assembly in both the steady-state operation and variable frequency operations. Compared with the widely adopted IGBT based ANPC converter in MV applications, the proposed 7-L hybrid inverter system features higher power efficiency, reduced harmonics, higher dc voltage utilization, reduced CMV and lower dv/dt, while remains cost effective compared to the solution using MV SiC MOSFETs.

Optimum 7 MW HTS direct-drive wind turbine synchronous generator designs with different rotor and stator iron topologies

Partially superconducting direct-drive wind turbine generators with high-temperature superconducting excitation winding enable an increase of the rated unit power, higher efficiency, and a high, adjustable power factor. The high excitation ampere-turns allow for iron topologies that differ from conventional permanent magnet-excited generators. This study compares four different iron topologies for 7,mathrm{MW} rated power and 8.33 rpm with a slotted stator or stator air gap winding regarding technical key characteristics and economic aspects. The generator designs are numerically optimized based on 2D finite element simulations. Maximum efficiency and the most lightweight designs are obtained with the stator air gap winding, whereas all-iron topologies prove advantageous regarding the trade-off between small active mass and high-temperature superconductor material consumption. The costs of the cryogenic cooling system and of the full converter are both found to be less than 15% for a wide range of generator designs.

Impacts of Inverter-Interfaced Wind Power Plants in the Phase-Selection and Directional Protection Functions

Considering the increasing insertion of Inverter-Interfaced Wind Power Plants (IIWPP) in modern power systems, this paper evaluates the impacts of this generation type on directional and phase selection functions. Six algorithms not yet explored in the context of IIWPP were evaluated, considering Full-Converter (FC) and Doubly-Fed Induction Generator (DFIG) topologies. For the studies, an IIWPP was modeled in detail using the Matlab/Simulink software. Contingency scenarios varying the type, resistance, and fault location have been simulated on a transmission line that connects the IIWPP to the primary grid. Thus, it was possible to report in detail the operational particularities of IIWPP that impact such functions, besides providing recommendations about the characteristics that these algorithms should contemplate to satisfactorily operate in systems with the presence of FC and DFIG generators.

Das ÖBB‐Kraftwerk Tauernmoos – Energiespeicher für die Bahn

AbstractIn 2004, ÖBB‐Infrastruktur AG started the first studies for the construction of a pumped‐storage hydro power plant between the two largest reservoirs of the existing Stubach Valley power plant group in Salzburg's Pinzgau region. Two reversible pump‐turbine units including a full converter with a total capacity of 170 MW and a maximum flow of 80 m3/s are planned. The construction of the 335 million. euro project started in 2020 and will be completed by autumn 2025. In addition to a 50,000 m3 cavern, an 11.5 km tunnel system including the access tunnels and the power water ways have been built. Most of the 11.5 km tunnel system is situated in stable gneiss. A greater challenge is the construction of the two inlet and outlet structures in the high mountain region during the winter season, when the lakes can be held on the lowest reservoir level. Since the remaining construction work is also carried out at an altitude of 1500 to 2250 m above sea level in alpine terrain, the construction company has been facing recurring problems such as snow, cold, wind, mudslides and the associated logistical difficulties. Despite these challenges, the excavation work was completed in summer 2022. The main focus is currently placed on the concrete works in the cavern, which is scheduled to be completed in autumn 2023. This will be followed by the installation of mechanical and electrical equipment as well as the control systems.

Black Start and Voltage Establishment Strategy for PMSG-Based Wind Turbine

During the black start, backup ac power sources such as diesel generators can offer line-side voltage reference for wind turbine and keep line-side converter of wind turbine work properly so that the dc-link capacitor voltage within converter can be established without overcharge. This study proposes a black start control strategy and line-side voltage establishment method for PMSG-based wind turbines with no ac power source. Unlike the traditional control strategy of full power grid-connected converters, the dc-link voltage within back-to-back full power converters of wind turbines can be controlled by generator-side converters, and the line-side voltage can be established by line-side converters with the help of fixed loads. The mechanical power can be balanced by pitch angle control, and the power unbalance between mechanical power and electrical power will be reflected in the rotor speed of PMSG. By this method, a single wind turbine can establish the line-side voltage with no extra backup ac power source, offering voltage reference for the other wind turbines during the black start of a wind power plant.

Hybrid DC-DC Converter with Low Switching Loss, Low Primary Current and Wide Voltage Operation

A full-bridge converter with an additional resonant circuit and variable secondary turns is presented and achieved to have soft-switching operation on active devices, wide voltage input operation and low freewheeling current loss. The resonant tank is linked to the lagging-leg of the full bridge pulse-width modulation converter to realize zero-voltage switching (ZVS) characteristic on the power switches. Therefore, the wide ZVS operation can be accomplished in the presented circuit over the whole input voltage range and output load. To overcome the wide voltage variation on renewable energy applications such as DC wind power and solar power conversion, two winding sets are used on the output-side of the proposed converter to obtain the different voltage gains. Therefore, the wide voltage input from 90 to 450 V (Vin,max = 5Vin,min) is implemented in the presented circuit. To further improve the freewheeling current loss issue in the conventional phase-shift pulse-width modulation converter, an auxiliary DC voltage generated from the resonant circuit is adopted to reduce this freewheeling current loss. Compared to the multi-stage DC converters with wide input voltage range operation, the proposed circuit has a low freewheeling current loss, low switching loss and a simple control algorithm. The studied circuit is tested and the experimental results are demonstrated to testify the performance of the resented circuit.

Electromagnetic Compatibility Analysis and Optimization Design of Switching Power Supply Printed Circuit Board

Printed Circuit Board (PCB) is not only an important electrical module of information equipment, but also an important source of electromagnetic radiation. Only when PCB works normally and is compatible with other electrical equipment, the whole information equipment can work normally. Because of the complexity of PCB structure and the difficulty of modeling, the EMC (Electromagnetic Compatibility) analysis of PCB is very difficult. For this reason, Taking the widely used full bridge current double rectifier converter as an example, aiming at the electromagnetic compatibility problems caused by the PCB design of the switching power supply, this paper proposes a simulation method based on the electromagnetic field by establishing the near-field radiation model of the PCB, analyzes the areas with high radiation intensity in the PCB layout, by optimizing the layout and wiring of the PCB, the electromagnetic compatibility performance of the switching power supply is improved. The simulation results show that the near-field radiation characteristics of PCB can be predicted by introducing the electromagnetic field simulation method in the design stage, according to the characteristics of the magnetic field, the optimal design is realized, so that the EMC of the switching power supply reaches the standard, and finally the working performance of the switching power supply is improved.

CertBench: conclusions from the comparison of certification results derived on system test benches and in the field

This paper presents measurement results of the world wide first successful certification the electrical properties of a wind turbine, solely based upon measurements obtained at a system test bench with HiL-System and grid emulator. For all certification relevant tests the results are compared to field measurements. The impact of the real-time models in the HiL-System as well as the converter-based grid emulator are discussed in this paper. For full converter wind turbine, different requirements for the model depth could be determined depending on the tests. Nevertheless, higher-quality models that reflect the plant behaviour better are recommended to reduce uncertainties within the certification process. This paper also shows that especially for grid failure events grid emulators require real-time impedance control, in order to emulate grid failures properly. Based on these findings, recommendations for the requirements on test bench components are formulated in this paper, in order to contribute to new certification guidelines. Overall, we conclude that based on the experiences made at two different system test benches, the vast majority of certification measurements can be carried out without limitation at such system test benches.

Dual-Active-Bridge Isolated DC–DC Converter With Variable Inductor for Wide Load Range Operation

This article explores the use of a variable inductor as a reactive element for energy transfer in a dual-active-bridge (DAB) converter. By using a controlled variable inductor, the optimal switching region in the operation of the phase-shift DAB can be extended, and thus, high efficiencies can be achieved over wider load ranges compared to the traditional solution. Moreover, the combined use of the variable inductance together with the phase shift, as two control parameters, allows for the linearization of the DAB converter transfer function, which improves the stability and the performance of the controller. And finally, due to the controlled saturation of the device, it is feasible to reduce the magnetic core size, yielding a size optimization of the full converter. This article develops a circuit-based model to simulate the converter system, aiming to study the proposed improvements. Furthermore, a 2-kW SiC-based DAB converter prototype is constructed, including a controlled variable inductor. The experimental results presented in this article validate the studies carried out for the different operation conditions.

A Technical & Economic Evaluation of Inertial Response From Wind Generators and Synchronous Condensers

Frequency stability in today's power systems has become more critical than ever due to the growing contribution of renewable energy sources. This situation has arisen because of the electro-mechanical decoupling between renewable generation sources and the main grid caused by their connection through power electronic converters. This paper designs two synthetic inertia controllers that adhere to the grid code requirements from two different countries and then to utilize them to aid in the integration of high levels of wind power penetration in a test power system. The controllers are designed for a full converter wind turbine generator and are validated in an EMT real-time simulation with isolated testing at different wind speeds and different wind power penetration. The role of synchronous inertia in maintaining frequency stability is also explored through the use of synchronous condensers. Finally, the economic aspect of inertia is discussed, using the real-world example of the Bornholm island power system.

A Robust Virtual Inertia Control of Battery Storage System to Enhance Transient Stability of Grid System including Wind Farms

With the rising penetration of modern converter-based wind farm (WF) into the existing grid system deteriorates system inertia due to reduction of the capacity of conventional power stations which may lead to the frequency instability as well as power system transient instability. In order to solve this concern, this paper presents a robust virtual inertia control approach for battery storage system (BSS) to enhance the frequency stability of the grid system after the generation failure owing to severe grid disruption. The control approach integrated inertial controller based on the rate of change of frequency (ROCOF) and droop controller according to frequency deviation. The impacts of the proposed virtual inertia controller (VIC) is confirmed through simulation analysis on a multi-machine power system with conventional power stations, permanent magnet synchronous generator (PMSG) with full converter based WF and squirrel cage induction generator (SCIG) based WF. Simulation study clearly demonstrates that by adopting both strategies, the BSS can effectively minimize the frequency nadir and steady-state error.

Wind energy conversion system under asymmetrical voltage failures: Analysis and nonlinear control

AbstractThis work presents the analysis and proposes nonlinear controls of a wind energy conversion system (WECS) to pass through symmetrical and asymmetrical voltage failures. The WECS is equipped with a nonsalient pole permanent magnet synchronous generator (PMSG) and two full converters, synchronous generator side converter (SGSC) and grid side converter (GSC), joined by a direct current (DC) link. As a consequence of the strong disturbances considered, a general strategy based on grid voltage values changes control references at SGSC and GSC. This strategy uses two flags for indicating normal grid voltages, symmetrical faults, or asymmetrical ones. Then, while control laws deal with model uncertainties and fast disturbances due to wind gusts, the strategy changes references to surpass strong, probably unbalanced, grid voltages disturbances. To assure robust properties, controllers are designed via a conjunction of Lyapunov and passivity theories. The proposed controllers and the strategy are tested under realistic wind conditions, uncertain parameters, and strong voltage disturbances.

Effects of Grid Frequency Drop on the Dynamic Performance of Full Converter Wind Turbine Generator

Recently, wind turbine generators connected to the grid is increased significantly. It has reached about 540 GW worldwide installation in the mid of 2018. One of the popular wind turbine types is Full Converter Wind Turbine Generator (FCWTG). It has a capability in extracting more energy compared to fixed speed type and also could contribute some amount of reactive power when the grid is required. Although frequency deviation rarely occurs in a grid side, it might be important to investigate the effects to FCWTG as FCWTG is very sensitive to a grid fault. In this paper, a deviation of frequency at the grid side is applied to investigate the dynamic performance of FCWTG during the rise and down frequency at the grid side. The system under study is carried out using Matlab/Simulink and the simulation results show that the grid frequency drop of 47.5 Hz has been started to cause the unstable dynamic performance of FCWTG. The worse scenario of grid frequency drop of 45 Hz could even lead the FCWTG to get damage.

Improved Faulted Phase Selection Algorithm for Distance Protection under High Penetration of Renewable Energies

The high penetration of renewable energies will affect the performance of present protection algorithms due to fault current injection from generators based on power electronics. This paper explains the process followed for analyzing this effect on distance protection and the development of a new algorithm that improves its performance in such a scenario. First of all, four commercial protection relays were tested before fault current contribution from photovoltaic system and full converter wind turbines using the hardware in the loop technique. The analysis of results obtained, jointly with a theoretical analysis based on commonly used protection strategy of superimposed quantities, lead to a conclusion about the cause of observed wrong behaviors of present protection algorithms under a high penetration of renewables. According to these conclusions, a new algorithm has been developed to improve the detection of faulted phase selection and directionality on distance protection under a short circuit current fed by renewable energy sources.

Analysis of Impact of Harmonic Disturbances on the Mechanical System of Wind Turbine

Abstract This paper analyzes the influence of harmonic frequencies on mechanical parts of wind turbines. Pitch system and drive train behavior of both doubly fed induction generator (DFIG) and full converter (FC) based wind turbines will be analyzed in detail.

Comparative Study on Thyristor and Rectifier Circuit Based DC Motor Control with Improved Power Factor and Total Harmonic Distortion

DC motor is used in many industrial applications. Because it has versatile control characteristics. With the increasing use of power semiconductor units, the speed control of the DC motor is increasingly getting sophisticated and precise. The DC motor can control by various methods, which is as field control, armature voltage control, armature resistance control. The speed of the DC motor is controlled by controlling the armature voltage. Armature voltage is controlled using different single-phase AC/DC converter. Half converter, semi converter, full converter, and dual converter are some of the thyristor-based circuits, which are used for speed control of DC motor. But using power electronics devices causes power factor and total harmonics distortion problem. Different types of Rectifier circuit with filter capacitor is used to reduce the problem of power factor and total harmonics distortion like Conventional single-phase diode rectifier with filter capacitor, single-phase diode rectifier with LC filter, single-phase diode rectifier circuit with series input resonant filter, Single phase diode rectifier circuit with improved parallel input resonant filter. In this paper, we do a comparative analysis of controlling DC motor with improved PF and THD.

Strong Resonance Investigation and Suppression in PMSG integrated Power Systems

Permanent magnet synchronous generators (PMSGs) with full converters have been widely used in wind power generation due to its superior flexibility and controllability. However, under some circumstance, the oscillation modes of PMSG (POMs) may excite strong resonance with the electromechanical oscillation modes (EOMs) of the power system that degrades the power system small signal stability. In this paper, A two-open-loop subsystem model is firstly derived to analyze the oscillation modes. Then the POMs are investigated with modal analysis, the relationship between POMs and related controllers are clarified. On this basis, the strong resonance between PMSG and the external power system is revealed and identified. Furthermore, a five-step parameter tuning method is proposed to relocate the position of POM as well as suppress the strong resonance. Both modal analysis and time-domain simulations validate the effectiveness of the proposed method.

Cause, Classification of Voltage Sag, and Voltage Sag Emulators and Applications: A Comprehensive Overview

The large-scale application of wind power and photovoltaic power solves the energy crisis and alleviates the environmental problems caused by the use of conventional energy. However, they are at risk of being randomly tripped from the network when faced to voltage sag and severe fault events, which will lead to a sudden reduction of active power output and also complicates fault recovery process of the whole system. Moreover, it may also aggravate failures and lead to large-scale power outages, which stimulates a growing interest in analyzing the low-voltage ride-through (LVRT) capabilities of the renewable energy systems (RES) and improving the performance through developing various mathematical models and analysis tools. In this paper, a systematical overview of cause, classification of voltage sag phenomena and voltage sag emulating techniques is presented, and four voltage sag generators (VSGs) are discussed and compared, which include generator based-VSG, shunt impedance based-VSG, transformer based-VSG and full converter based-VSG. Furthermore, a closed-loop detection platform based on real-time digital simulator (RTDS) for the converter controller of a permanent magnet synchronous generator (PWSG) set is introduced, to investigate the LVRT performance of the WT system under grid voltage sag conditions. Finally, the application of VSG in RES are presented and the future research directions are also discussed.